Compound movement centrifugal ball-mill



Feb. 24, 1959 F. LIME 2,874,911

COMPOUND MOVEMENT CENTRIFUGAL BALL-MILL Filed May 2Q, 1955 2 Sheets-Shet 2 FM NK L :MB

4 n0g/ws ,United States Patent O 'z,s74,911 l VcoMroUND MOVEMENT CENTRIFUGAL BALL-MILL A Frank Limb, Harrogate, England Application May 20, 1955, Serial No. 509,898 s claims. (ci. 2411-175) This invention relates to ball -mills and like rotary chamber apparatus by which is meant rotary chamber apparatus in general for milling, dispersing, mixing, or similarlyftreating materiahthe chamber or chambers usuallycontaining balls, pebbles, sand or other grinding media, although with some materials grinding media may not be required, the treatment being elected by the movement of the material itself in the rotary chamber.

Most ball `millsin `use comprise `oneuorrnore chambers which rotateyabota Afixed axis,` usually horizontal, although vertical or inclined axis mills are known and mills having -a compound motion, such as a planetary motion of mill chambers, havebeen proposed. ,l

The efficiency of a ball mill, in terms of the rate at which given treatment of material can be completed, depends upon the total area of contact, relative movement and pressure which can be achieved between the active surfaces of the charge and the mill chamber, that is to say between the surfaces of the material treated and of the grinding media,` mill chamber surface, or other coacting surfaces.

` In `a single fixed axis mill, the rate of operation is limited by the so-called critical speed above `which the charge, of material and grinding media, becomes an internally stationary mass lining the wall of the mill chamber under the action of centrifugal force.

With a planetary `motion mill the critical speed limit can be overcome, so as to retain internal movement in the charge at high speeds, but the mill construction and mechanism is necessarily more elaborate than for a single fixed axis mill and there is a loss in economic eiliciency in terms of the overall size of the apparatus for a given capacity.

The object of the present invention is to provide a ball mill or like apparatus which is not subject to a critical or limiting speed of rotation and which will give high efficiency in terms of rate and degree of treatment combined with an economic eiciency in terms of the capacity of the apparatus.

According to the invention, a ball mill or like rotary chamber is arranged to rotate about its own axis and simultaneously revolve about a substantially parallel fixed 2,874,911 i Patented Feb.` 72,4, 1959 sure of and within the charge depend upon the difference `between the centrifugal forces to which the components of the charge are subjected due to the motion about the two axes respectively and this difference in turn depends upon the angular speed and mean radius of the charge with respect to each axis. The difference could therefore be altered by altering either the radius `of the mill chamber, the separation of the two axes, the rates of revolution and rotationlor the volume of the charge in relation tothe volume of themill chamber. p

Of the above-mentioned factors, the most important, from a practical point of view, are the radius of the mill `chamber and the separation of the two axes because in a given mill these must be predetermined whereas the other vfactors can be varied relatively easily.

`The wider the ratio between the radius of the mill chamber and the separation of the two axes, then the greater the capacity of the mill in comparison with its overall size.

I believe that the internal movement which takes place in the charge of a mill in accordance with my invention consists largely of rolling shear between the wall of the chamber and the grinding media and between the grinding media themselves and that such rolling shear under the contact pressure appropriate to the material under treatment is the most effective form ofinternal movement which can be produced in a mill charge.

The rolling shear motion arises from the` fact that Whereas the grinding media are thrust against the wall of the chamber under the action of centrifugal force from the motion about both axes, that due to revolution of the chamber about the fixed axisis the greater andthere is a consequent relative movement between the media and the wall of the chamber rotating about its own axis. This relative movement drives the grinding media to rotate in contact with the wall chamber and with each other with opposite directions of relativemovement `at axis, the separation of the two axes being appreciably less than the radius of the chamber.

Preferably the separation of the two axes is small in relation to the radius of the chamber itself and the revolution of the chamber, about the fixed axis, is opposite to and of higher rate than the rotation of the chamber, about its own axis.

The resultant effect on the charge of a mill chamber having a compound motion about two relatively closely spaced axes in vaccordance with the Ainvention is that the charge more or less lines the wall of the chamber but the charge retains a high rate of movement both as a whole relatively to the surface of the chamber and within the charge in the form of relative movement of its components.

The rate of relative movement and the contact prespoints of Contact.

The material of the charge itself is of course subject to the same action as that undergone by the grinding media and in addition is subject to the shear between the contacting surfaces of the grinding media with each other and with the chamber wall.

The invention is particularly suitable for vertical axis, cylindrical chamber mills but is also applicable to mills having inclined or horizontal axes and chambers of circular cross-section symmetrical about the rotational axis of the chamber, other than cylindrical, for instance globular or bowl-shaped chambers.

One embodiment of the invention applied to a vertical axes cylindrical -ball mill will now be described, solely by way of example, with reference to the accompanying drawings, in which:

Fig. 1 is a vertical axial section through a mill,

Fig. 2 is a horizontal transverse section on the line II--II of Fig. l,

Fig. 3 is a plan, and

Fig. 4 is a vertical axial section along the line F-F of Fig. l.

In the mill illustrated, the mill chamber is a pot 1, of porcelain for example, clamped in a cage 2 by screwdown wedges 3 and having a lid 18L secured by a spider 4 and screw 5. In the pot 1 is placed the charge consisting of balls or other grinding media and the material,

,such as paint, to be treated.

The cage 2, perforated to promote dissipation of heat from the pot, has a bottom stem journal 6 supported in a step bearing 7 and a top circumferential roller bearing 8 so that the cage, and therewith the pot, can rotate about the orbital axis C-C of the pot or mill chamber relatively to a carrier cylinder 9.

The cylinder 9 itself has a bottom stem journal 10 Y 3'Y supported in a step bearing 11 and a top circumferential roller bearing 12 so that the cylinder, and therewith the cage 2 can rotate about a fixed axis F-F in a `stationary' mill' casing' or'housing 13.

On the housing 13 is mounted an electric motor 14 with a' driving belt 15 to' a pulley Wheel 16 fast on the base of thecylinderl 9'; Mounted fast on a socket pedestal17 around the stem journal 10 of the cylinder 9 is` a iixed gear wheel 18` which meshes with an intermediate pinion 19 journalled in the hub 16a of the pulley wheel 16 as'seen in Fig. 4 and mounted on the same shaft with pinion'19 isa second gear meshing with a gear wheel 20 fast on the stern journal 6A of the vcage 2. The hub 16L servesl as a box for the gears and can be oil-filled.

When they cylinder 9y isdriven, by the motor 14, belt 15 and pulley wheel 16, to rotate about the fixed axis F-F, the intermediate pinion 19 runs round the fixedv gear wheel 18 and transmits to thegear wheel 20 a drive-which turns the cage 2 about the orbital axis C--C within the cylinder 9 and in the opposite direction to the rotation of the cylinder 9, as indicated by the arrows in Figs. 2 and 3.

It will be seen that as a result of the drive, the mill chamber or pot 1 revolves about the iixed axis F--F whilst rotating about itsk own, orbital, axis C-C and that the radius x of revolution of the chamber, given by the separation of the two axes, is appreciably less than the radius y ofthe chamber itself.

In order to maintain dynamic balance when the mill is running, a balance weight 21 is provided inthe cylinder 9 diametrally'opposite to the cage 2.

I claim:

l. A ball mill comprising a stationary vertical cylindrical housing', a central bearing' in the' base of said housing, a circumferential bearing around the top of said housing, a cylindrical carrier in said housing and rotatably mounted about a iirstl xed vertical axis Within said bearings whereby all bearings of said carrier are exterior thereof, a vertical axis cylindrical cage, a cylindrical ball mill chamber coaxially disposed within and supported by the base portion of said cage, said cage being rotatably mounted in said carrier` on aV second vertical` axis spaced radially from said first axisn at a distance appreciably less than the radius of said chamber, means for rotating said carrier about said first axis, and means for rotating said cage about said second axis simultaneously with rotation of said carrier about said rst axis.

2. A ball mill as claimedbyv claim l, in which said cage has a bottom stem journal and a top bearing rim and said carrier has aliottom. bearing for said journal and a top circumferential bearing for said rim whereby said cage above the base supporting portion is rotatably mounted about said, second axis and the interior of said cage above the base supporting portion is of substantially constant diameter'V and slightly larger than said ball mill chamber whereby said -ball mill chamber may be inserted and removed from above said cage.

3. A ball mill as claimed by claim 1,. in whichA said means for rotating said cage comprise a lirst'gear wheel in said housing fixedly mounted on said central bearing on said first axis, a second gear Wheel mounted ,onv said cage, and an intermediate pinion journalled in said cylin drical carrier and meshing with both said gear wheels whereby rotation of said carrier about said first axis causes rotation of said cage about said second axis.

References Cited'I in the me of this patent UNITED STATES PATENTS OTHER REFERENCES,

New-Type of Grinding Mill, by Fahrenwald, pages* 93,

94 and 9,5 to Gyratory Ball Mill, Rock Products, February 1951. 

